In reinforced concrete construction, it is necessary to support the reinforcing bars (xe2x80x9crebarsxe2x80x9d) in their designated locations during placement of the concrete and thereafter as it cures. This is accomplished in its most rudimentary form by simply resting the rebar on pieces of concrete placed on the form surface. Obviously, this approach may be unsatisfactory for many reasons, such as the lack of any means for fixing the rebar at their designed positions, as a result of which the rebar may be displaced as the concrete is poured.
In response to the shortcomings of this method of supporting rebar, welded wire supports have been developed and are used extensively in the reinforced concrete construction industry. For example, U.S. Pat. No. 4,689,867 is directed to a welded wire rebar of one type, while U.S. Pat. No. 4,996,816 describes another welded wire rebar support design. With metal supports, however, there is a potential problem of corrosion. Coating the wire with epoxy is a method of dealing with this problem, but coating is expensive, and if the coating is damaged, corrosion may still occur.
Plastic supports are generally non-corrodible and therefore overcome the problems noted above with welded wire supports, but they usually lack the open construction provided by wire supports that permits full flow of concrete through and around the support during concrete placement. While U.S. Pat. Nos. 5,729,949 and 6,089,522 disclose supports that may be formed of plastic and have openings formed in them to facilitate concrete placement, the supports shown in these patents are individual units as opposed to supports that may extend for several spans. U.S. Pat. No. 5,664,390 discloses a plastic bolster that may extend across several spans and uses a pair of spaced legs and a control body that resists deformation through the use of pin-like projections that bite into the underlying surface.
The above-noted problems associated with prior art bolsters are obviated by the bolster of the present invention. Specifically, the bolster of the present invention is preferably molded of non-corrodible plastic, is of inverted T-shape for greater stability, and provides an open construction that facilitates distribution of concrete during placement through and around the bolster.
The base of the bolster of the present invention may be molded integrally with the rebar support section that projects substantially perpendicularly away from an upper surface of the base and terminates in a rebar-engaging cap that extends in generally parallel relationship to the base. Both the base and the support section may be of truss-like construction, which results in a high weight-to-strength ratio, with a major portion of the base and web being occupied by voids, thereby enhancing concrete flow through and around the bolster.
In another preferred embodiment of the invention, the base may be molded with a series of posts spaced along and projecting from an upper surface and a rebar-engaging cap molded separately and mechanically interconnected to outer ends of the posts by means of joint elements molded in the posts and the cap. The latter may also be provided with transverse ridges on its outer rebar-engaging surface to break up shear planes. Additionally, the junctures of the posts and the base are strengthened by gussets that project upwardly from the base and extend both longitudinally and laterally of the base upper surface. To further strengthen the bolster, opposite longitudinal edges of the base are provided with continuous upstanding ribs, and the ribs and gussets further serve to break up shear planes.
The post construction of this embodiment is conducive to flexible injection mold tolling that can mold a wide range of sizes without the need for different molds for each size. The portions of the mold that forms the posts are simply adjusted.
The bolster of the present invention may be utilized separately, or in a preferred form of the invention, may be provided with complementary buckles at opposite ends to permit connection with like units to form a continuous bolster of desired length. In this regard, both the base and the rebar support section are each provided with complementary buckles so that the units, when interconnected, are joined at both their upper and lower extremities, thereby enhancing the strength and stability of the composite bolster.
In either case, that is, whether formed as discrete units or with interconnecting buckles, the bolsters may be formed of any convenient length to suit a desired application. In a preferred embodiment, the length is selected to facilitate handling and storage, e.g., about 2.5 feet in length. The inverted T-shape of the units, which permits the units to be nested, and the convenient unit length, greatly facilitate packaging the units for shipment.
The bolsters of the present invention may be formed from a variety of plastics, such as polycarbonate/acrylonitrile butadiene styrene (ABS), polyproylene, nylon, or ABS. Additionally, the plastic may be reinforced with a variety of fibers, such as fiberglass, Keviar, carbon fibers, or metal fibers.
These and other features and advantages of the bolster of the present invention will become more apparent from the following description.